1. Field of the Invention
The present invention is in the field of small molecule inhibitors of HCV and methods of using them to inhibit HCV.
2. Summary of the Related Art
The hepatitis C virus (HCV) is one of the most important causes of chronic liver disease in the United States. It accounts for about 15 percent of acute viral hepatitis, 60 to 70 percent of chronic hepatitis, and up to 50 percent of cirrhosis, end-stage liver disease, and liver cancer. Almost 4 million Americans, or 1.8 percent of the U.S. population, have antibody to HCV (anti-HCV), indicating ongoing or previous infection with the virus. Hepatitis C causes an estimated 8,000 to 10,000 deaths annually in the United States.
A distinct and major characteristic of hepatitis C is its tendency to cause chronic liver disease. At least 75 percent of patients with acute hepatitis C ultimately develop chronic infection, and most of these patients have accompanying chronic liver disease.
Chronic hepatitis C varies greatly in its course and outcome. At one end of the spectrum are patients who have no signs or symptoms of liver disease and completely normal levels of serum liver enzymes. Liver biopsy usually shows some degree of chronic hepatitis, but the degree of injury is usually mild, and the overall prognosis may be good. At the other end of the spectrum are patients with severe hepatitis C who have symptoms, HCV RNA in serum, and elevated serum liver enzymes, and who ultimately develop cirrhosis and end-stage liver disease. In the middle of the spectrum are many patients who have few or no symptoms, mild to moderate elevations in liver enzymes, and an uncertain prognosis. Researchers estimate that at least 20 percent of patients with chronic hepatitis C develop cirrhosis, a process that takes 10 to 20 years. After 20 to 40 years, a smaller percentage of patients with chronic disease develop liver cancer. The therapy of chronic hepatitis C has evolved steadily since alpha interferon was first approved for use in this disease more than ten years ago. At the present time, the optimal regimen appears to be a 24- or 48-week course of the combination of pegylated alpha interferon and ribavirin.
Two forms of peginterferon have been developed and studied in large clinical trials: peginterferon alfa-2a (Pegasys®: Hoffman La Roche: Nutley, N.J.) and peginterferon alfa-2b (Pegintron®: Schering-Plough Corporation, Kenilworth, N.J.). These two products are roughly equivalent in efficacy and safety, but have different dosing regimens. Peginterferon alfa-2a is given subcutaneously in a dose of 180 mcg per week. Peginterferon alfa-2b is given subcutaneously weekly in doses of 1.5 mcg per kilogram per week (thus in the range of 75 to 150 mcg per week).
Ribavirin is an oral antiviral agent that has activity against a broad range of viruses. By itself, ribavirin has little effect on HCV, but adding it to interferon increases the sustained response rate by two- to three-fold. For these reasons, combination therapy is now recommended for hepatitis C and interferon monotherapy is applied only when there are specific reasons not to use ribavirin.
Ribavirin is an oral medication, given twice a day in 200-mg capsules for a total daily dose of 800 to 1,200 mg based upon body weight and the form of peginterferon. When combined with peginterferon alfa-2b, the recommended dose of ribavirin is 800 mg per day. When combined with peginterferon alfa-2a, the dose of ribavirin is 1,000 mg for patients who weigh less than 75 kilograms (165 pounds) and 1,200 mg for those who weight more than 75 kilograms. In all situations, ribavirin is given in two divided doses daily.
At the present, peginterferon alfa-2a has not been approved for use in chronic hepatitis C in the United States and is available only in clinical trials. Thus, only peginterferon alfa-2b is available for general use.
Combination therapy leads to rapid improvements in serum ALT levels and disappearance of detectable HCV RNA in up to 70 percent of patients. However, long-term improvement in hepatitis C occurs only if HCV RNA disappears during therapy and stays undetectable once therapy is stopped. Among patients who become HCV RNA negative during treatment, a proportion relapse when therapy is stopped. The relapse rate is lower in patients treated with combination therapy compared with monotherapy. Thus, a 48-week course of combination therapy using peginterferon and ribavirin yields a sustained response rate of approximately 55 percent. A similar course of peginterferon monotherapy yields a sustained response rate of only 35 percent. A response is considered “sustained” if HCV RNA remains undetectable for six months or more after stopping therapy.
The optimal duration of treatment varies depending on whether interferon monotherapy or combination therapy is used, as well as by HCV genotype. For patients treated with peginterferon monotherapy, a 48-week course is recommended, regardless of genotype. For patients treated with combination therapy, the optimal duration of treatment depends on viral genotype. Patients with genotypes 2 and 3 have a high rate of response to combination treatment (70 to 80 percent), and a 24-week course of combination therapy yields results equivalent to those of a 48-week course. In contrast, patients with genotype 1 have a lower rate of response to combination therapy (40 to 45 percent), and a 48-week course yields a significantly better sustained response rate. Again, because of the variable responses to treatment, testing for HCV genotype is clinically useful when using combination therapy.
In view of the foregoing, there is a desire for alternative, more effective agents for treating HCV infection.